Slaughter House

Hey, Guys.
A mission in minecraft is to create a slaughter house, a cool machine that kills mobs such as creepers and zombies and anything you want.
1. Set traps using cacti for killing animals like cows and pigs and chicken.
2. Make TNT execuetion rooms made of obsedian and TNT. Step on a pressure plate to detonate the TNT, killing the mobs inside the room. Recomended for villagers and zombies.
3. Dispenser traps that shoot fire arrows. Put lava in front of the dispenser to make the arrows be on fire. For any mobs you like.
4. Lava room. Kills anything.

However, there here are some exceptions of mobs that might not die in specific slaughter houses.
1. Nether mobs do not burn to death, so a zombie pigman, ghast, blaze and wither skeleton. However, water is useful against blazes.
2. Withers basically blow up everything the skulls touch, except for bedrock, so a slaughter house for this mob will be quite hard to build. The wither will have to suffocate to death or drown. Pouring lava over it will not get you the nether star. The slaughter house for drowning must be made of bedrock. Make a trap where the wither cannot move but can only blow up the blocks around it. Then pour water from the top part of the trap. It will slowly drown. Look at the picture below for reference.
PICTURE TO BE UPLOADED.